I. What is Neuropathic Pain?

Neuropathic pain refers to chronic pain caused by damage or dysfunction within the nervous system itself, distinct from common inflammatory or tissue-injury pain (e.g., arthritis, trauma).The International Association for the Study of Pain (IASP) defines it as pain arising as a direct consequence of a lesion or disease affecting the somatosensory nervous system.

It frequently manifests as spontaneous pain (triggered without external stimuli), hyperalgesia (severe pain evoked by mild stimulation), or allodynia (pain induced by normally non-noxious stimuli such as light touch).

Typical Symptoms

1. Burning, electric-shock or stabbing sensations

2. Numbness or tingling (a sensation like ants crawling on the skin)

3. Abnormal sensitivity to hot and cold temperatures

4. Worsening pain at night

II. Common Etiology and Classification

The causes of neuropathic pain are complex, mainly categorized as follows:

1. Peripheral Nervous System Injury

1. Diabetic peripheral neuropathy: Persistent hyperglycemia damages nerves, leading to burning pain in the feet.

2. Postherpetic neuralgia: Viral injury to nerve fibres results in persistent pain after skin rashes heal.

3. Traumatic or postoperative nerve injury: including phantom limb pain following amputation and nerve damage at surgical incisions.

2. Central Nervous System Lesions

1. Post-stroke pain: Thalamic or brainstem infarction causes pain on the contralateral side of the body.

2. Spinal cord injury: Abnormal nerve conduction triggers pain below the injury level.

3. Multiple sclerosis: Central demyelinating lesions induce sensory disturbances.

3. Other Causes

1. Chemotherapy-induced peripheral neuropathy (e.g., paclitaxel)

2. Compressive neuropathies such as trigeminal neuralgia and sciatica

III. Pathogenesis: Why Does Nerve Injury Trigger Pain?

The core mechanism of neuropathic pain is abnormal neural signal transmission, including:

1. Peripheral Sensitization

Damaged nerve fibres (C-fibres and Aδ-fibres) discharge abnormally and release abundant pain mediators (substance P, calcitonin gene-related peptide), amplifying nociceptive signals.

2. Central Sensitization

Increased excitability of spinal dorsal horn neurons leads to overinterpretation of pain signals transmitted to the brain. Pain persists even after peripheral stimuli disappear.

3. Neural Plasticity Changes

Cortical reorganization (e.g., the brain misinterprets signals from amputated limbs in phantom limb pain) or impaired function of the descending inhibitory system.

4. Ion Channel Dysfunction

Overexpression of sodium channels (Nav1.7, Nav1.8) or impaired potassium channel function causes abnormal neuronal excitability.

IV. Treatment: Multidisciplinary Comprehensive Management

Treatment aims to relieve pain and improve physical function, requiring combined pharmacological and non-pharmacological interventions.

1. First-line Medications

1. Antidepressants: Tricyclic antidepressants (amitriptyline) or SNRIs (duloxetine) to modulate descending inhibitory pathways.

2. Anticonvulsants: Gabapentin and pregabalin suppress calcium channels to reduce abnormal nerve discharges.

2. Second-line Medications

1. Topical lidocaine patches (indicated for localized neuropathy)

2. Opioids (e.g., tramadol; caution is required due to dependence risks)

3. Interventional Therapy

1. Nerve blocks (e.g., sympathetic nerve block)

2. Spinal Cord Stimulation (SCS) or Transcranial Magnetic Stimulation (TMS)

4. Non-pharmacological Therapy

1. Cognitive Behavioral Therapy (CBT) to ease pain-related anxiety

2. Physical therapy (e.g., Transcutaneous Electrical Nerve Stimulation, TENS)

V. Daily Self-Management Advice for Patients

1. Control underlying diseases (e.g., maintain target blood glucose levels in diabetes)

2. Avoid alcohol and tobacco (they exacerbate nerve damage)

3. Moderate exercise (e.g., yoga to improve neural plasticity)

Summary

Neuropathic pain is a complex chronic pain condition caused by "erroneous signals" within the nervous system and requires early intervention. Future research directions include ion-channel targeted drugs and nerve repair technologies.If unexplained persistent pain occurs, seek consultation with a pain department or neurology department promptly.

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